This invention relates to disabling circuits for television receivers.
The high voltage or ultor accelerating potential for a picture tube typically is derived by rectifying retrace pulses generated in the high voltage winding of a horizontal output of flyback transformer of the horizontal deflection circuit. High brightness color picture tubes may require the development of relatively large ultor accelerating potential. Care must be taken that the developed ultor potential not exceed safe operating levels in order to prevent the generation of excessive amounts of x-radiation.
Should the high voltage exceed predetermined levels, typical high voltage safety circuits incorporate latching circuits which shut down or disable normal deflection circuit operation and high voltage generation under these conditions.
The supply voltage for the latch should be derived from a voltage source which, during start-up or initial energization of the television receiver, will not cause the latching circuit to nuisance trip or erroneously energize. A supply source should be selected which would enable the latch to be deenergized after television receiver shutdown, in order to permit the operator to restart the television receiver. The supply source selected, however, should not enable the television receiver to automatically cycle between shutdown and start-up modes of operation, as harmful stresses may be applied to various television receiver elements such as the flyback transformer and the horizontal output transistor.